The Environmental Protection Agency (EPA) has estimated that a potential gap between future needs and current spending for wastewater infrastructure of $150 billion to $400 billion could occur over the next decade. A number of entities are involved in planning, financing, building, and operating this infrastructure. Some of these stakeholders have suggested a variety of approaches to bridge this potential gap. One such proposal is to establish a clean water trust fund. In this context, GAO was asked to (1) obtain stakeholders' views on the issues that would need to be addressed in designing and establishing a clean water trust fund and (2) identify and describe potential options that could generate about $10 billion in revenue to support a clean water trust fund. In conducting this review, GAO administered a questionnaire to 28 national organizations representing the wastewater and drinking water industries, state and local governments, engineers, and environmental groups and received 22 responses; reviewed proposals and industry papers; interviewed federal, state, local, and industry officials; and used the most current data available to estimate the revenue that could potentially be raised by various taxes on a range of products and activities. GAO is not making any recommendations. While this report identifies a number of funding options, GAO is not endorsing any option and does not have a position on whether or not a trust fund should be established. In designing and establishing a clean water trust fund, stakeholders identified three main issues that would need to be addressed: how a trust fund should be administered and used; what type of financial assistance should be provided; and what activities should be eligible to receive funding from a trust fund. While a majority of stakeholders said that a trust fund should be administered through an EPA partnership with the states, they differed in their views on how a trust fund should be used. About a third of stakeholders responded that a trust fund should be used only to fund the existing Clean Water State Revolving Fund (CWSRF), which is currently funded primarily through federal appropriations, while a few said it should support only a new and separate wastewater program. A few stakeholders supported using a trust fund to support both the CWSRF and a separate program, while others did not support the establishment of a trust fund at all. In addition, more than half of the stakeholders responded that financial assistance should be distributed using a combination of loans and grants to address the needs of different localities. Finally, although a variety of activities could be funded, most stakeholders identified capital projects as the primary activity that should receive funding from a clean water trust fund. A number of options have been proposed in the past to generate revenue for a clean water trust fund, but several obstacles will have to be overcome in implementing these options, and it may be difficult to generate $10 billion from any one option by itself. Funding options include a variety of excise taxes. In addition, Congress could levy a tax on corporate income. An additional 0.1 percent corporate income tax could raise about $1.4 billion annually. Congress also could levy a water use tax. A tax of 0.01 cent per gallon could raise about $1.3 billion annually. Regardless of the options selected, certain implementation obstacles will have to be overcome. These include defining the products or activities to be taxed, establishing a collection and enforcement framework, and obtaining stakeholder support for a particular option or mix of options.